In the conventional filament winding operation, a fibrous strand impregnated with a thermosetting resin is wound in a helical pattern in a number of superimposed layers on a mandrel to form a tubular article.
In one type of filament winding operation, a single band of webs or fibers is applied to the mandrel in a helical pattern, and depending on the width of the band and the winding angle, the turns or convolutions may be spaced apart in each pass along the length of the mandrel, in which case a cross-over pattern is obtained, or the side edges of the convolutions can be in abutting relation, in which case a continuous fibrous layer is obtained in each pass.
In another type of filament winding operation, a 360.degree. delivery of the fibrous strands is utilized, meaning that a multiplicity of strands are simultaneously applied to the mandrel at spaced locations throughout the entire circumference of the mandrel. In this type of delivery, the winding head has a circular configuration and is spaced radially outward of the mandrel and the strands pass through a radial slot in the winding head and are guided onto the outer surface of the mandrel. Rotation of the mandrel in combination with longitudinal advancement of either the mandrel or the winding head will cause the strands to be wound in a helical pattern on the mandrel.
At start-up of the winding operation of this latter type of machine, the multiplicity of fibrous strands are grouped together and wound manually in two or three turns about an end of the mandrel to lock the strands to the mandrel. After the strands are suitably locked to the mandrel, the winding operation can proceed. As the manually applied strands are bunched together, this portion of the wound article must be severed after completion of winding and scrapped. When utilizing a mandrel having a diameter in the range of 8 to 12 inches, about 24 inches of the end of the wound article is normally scrapped, resulting in a substantial waste of material.
As an added problem, the initial attachment of the multiplicity of strands to the mandrel at the start of winding is directly dependent upon the skill of the operator, and if some of the strands are not firmly attached to the mandrel, the entire winding pattern may be defective, with the result that the entire article must be scrapped. As the fibrous strands are normally coated with a thermosetting resin, the manual wrapping of the resin coated strands about the mandrel at the start of the winding operation is a messy and time-consuming task.
After completion of the wound article, the multiplicity of fibrous strands must be cut. Due to the tension on the strands, cutting, in some cases, will cause the strands to snap back through the head before a subsequent article can be wound. As the typical winding operation may contain up to 1500 separate strands, the rethreading of the strands is a very time-consuming operation.
Wind-off rings have been used in the past in filament winding systems, particularly in the winding of yarn on spools or creels. After completion of winding, the yarn is transferred to a wind-off ring, the yarn is severed, and the completed wound article can be removed and a new spool or mandrel inserted. The use of the wind-off ring eliminates the need of reattaching the yarn to the spool at the start of each winding operation.